Auxiliary ambient air refrigeration system for cooling and controlling humidity in an enclosure

ABSTRACT

An auxiliary ambient air refrigeration system for cooling and controlling humidity in an enclosure including a conventional refrigeration unit for providing cool refrigerated air to the enclosure, an auxiliary refrigeration unit for providing cool ambient air to the enclosure, a first sensor unit for sensing air temperature and humidity inside the enclosure, a second sensor unit for sensing ambient air temperature and humidity; and a controller responsive to the sensor units and their indicated dew points of the enclosure air and the ambient air for enabling the auxiliary refrigeration unit to provide cool ambient air to the enclosure when temperature inside the enclosure is above a first predetermined temperature, the ambient temperature is less than the enclosure temperature by a predetermined differential temperature and the dew point of the ambient air is matched to the dew point range of the air in the enclosure.

FIELD OF THE INVENTION

This invention relates to an auxiliary ambient air refrigeration system for cooling and controlling humidity of air in an enclosure.

BACKGROUND OF THE INVENTION

There have been a number of auxiliary ambient (outside) air refrigeration systems proposed. Some of these systems, such as those described in U.S. Pat. Nos. 4,175,401 and 4,023,947, employ a control system having a “changeover” thermostat that senses the outside temperature and de-energizes the conventional refrigeration system and energizes an outside air refrigeration system whenever the outside temperature falls below a predetermined temperature. Another control strategy for outside air systems is to have no electrical interconnection between the conventional refrigeration system and the outside air system. This type of “independent” system is found in U.S. Pat. Nos. 4,250,716, 4,178,770, 4,147,038, 4,619,114, 4,244,193, and 4,358,934. The operation of each of these outside air systems is controlled by two thermostats, one sensing the outside temperature and one sensing the temperature inside the enclosure. The thermostat controlling the operation of the conventional refrigeration system is set at a higher operating range than the thermostat sensing the enclosure temperature for the outside air system. The conventional refrigeration system does not operate as long as the outside air system can adequately cool the enclosure. The outside air thermostat is set at a predetermined cut-in temperature such that the outside air system will only be used when the outside air is cold enough to always be at least as efficient as the conventional refrigeration system. A differential thermostat senses the temperature of both the air inside the enclosure and the outside or ambient air, compares them, and actuates at least one fan or blower to circulate cool outside air so as to cool the inside of the enclosure. As long as the outside or ambient temperature is at least a pre-selected number of degrees cooler than the temperature inside the enclosure and this inside temperature is above a pre-selected cut-in temperature for the outside air refrigeration system, the outside air fan, or fans, circulate cool outside air until the temperature inside the enclosure falls to a pre-selected cut-out setting for the outside air system or until the enclosure temperature is cooler than a pre-selected number of degrees warmer than the outside air temperature, at which time the outside air fan, or fans turn off. See U.S. Pat. No. 5,239,834. However, there remains yet another issue: humidity. Too little can affect the quality of the contents, especially food products, for example. Too much humidity can also be a problem for such goods as well as other types of goods and may increase the cooling load, resulting in lower efficiency and can damage equipment.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide an improved, auxiliary ambient air refrigeration system for cooling and controlling humidity in an enclosure.

It is a further object of this invention to provide such an improved auxiliary ambient air refrigeration system which prevents the refrigerated air from being too dry or too humid while preserving and improving the efficiency of the cooling burden.

The invention results from the realization that an improved auxiliary ambient air refrigeration system for cooling and controlling humidity in an enclosure which prevents too much or too little humidity and improves efficiency can be achieved using a controller responsive to an inside the enclosure sensor unit and an ambient air sensor unit and their indicated dew points for enabling an auxiliary refrigeration unit to provide cool ambient air to the enclosure when the temperature inside the enclosure is above a first predetermined temperature, the ambient temperature is less than the enclosure temperature by a predetermined differential temperature and the dew point of the ambient air is matched to the dew point range of the air in the enclosure.

The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives.

This invention features an auxiliary ambient air refrigeration system for cooling and controlling humidity in an enclosure including a conventional refrigeration unit for providing cool refrigerated air to the enclosure, an auxiliary refrigeration unit for providing cool ambient air to the enclosure, a first sensor unit for sensing air temperature and humidity inside the enclosure, a second sensor unit for sensing ambient air temperature and humidity; and a controller responsive to the sensor units and their indicated dew points of the enclosure air and the ambient air for enabling the auxiliary refrigeration unit to provide cool ambient air to the enclosure when temperature inside the enclosure is above a first predetermined temperature, the ambient temperature is less than the enclosure temperature by a predetermined differential temperature and the dew point of the ambient air is matched to the dew point range of the air in the enclosure.

In a preferred embodiment the controller may be responsive to the sensor units for enabling the conventional refrigeration unit when the enclosure temperature is at a second predetermined temperature higher than the first predetermined temperature. The dew point range may include a minimum humidity dew point and the auxiliary refrigeration unit may not be enabled if the dew point of the enclosure air is at or below that minimum dew point and if the dew point of the ambient air is below the dew point of the enclosure air. The dew point range may include a maximum humidity dew point and the auxiliary refrigeration unit may not be enabled if the dew point of the enclosure air is at or above that maximum dew point and if the dew point of the ambient air is above the dew point of the enclosure air. There may be further included a humidifier and the controller may be responsive to a humidity below the minimum humidity dew point to enable the humidifier. The sensor unit may include a temperature sensor and a dew point sensor. The dew point range may include a minimum humidity dew point and the auxiliary refrigeration unit may not be enabled if the dew point of the ambient air is below that minimum dew point. The dew point range may include a maximum humidity dew point and the auxiliary refrigeration unit may not be enabled if the dew point of the ambient air is above that maximum dew point.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

FIG. 1 is a simplified diagram of an embodiment of the auxiliary ambient air refrigeration system of this invention;

FIG. 2 is a more detailed partial, cross sectional view with portions removed of an enclosure served by one embodiment of the auxiliary ambient air refrigeration system of this invention;

FIG. 3 is a schematic electrical diagram of the system of FIG. 2;

FIG. 4 is a logic block diagram illustrating humidity control using ambient air dew point control for minimum humidity criteria;

FIG. 5 is a logic block diagram illustrating humidity control using ambient air dew point control for maximum humidity criteria; and

FIG. 6 is a logic block diagram illustrating an alternative approach for humidity control combining maximum and minimum humidity logic.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.

There is shown in FIG. 1 one embodiment of an auxiliary ambient air refrigeration system 10 according to this invention for cooling and controlling humidity in an enclosure 12. The auxiliary ambient air refrigeration system 10 includes a conventional refrigerator unit 14 and an auxiliary ambient air refrigerator unit 16. There is an inside temperature/humidity (dew point) sensor unit 18 inside enclosure 12 and an outside or ambient air temperature/humidity (dew point) sensor unit 20 outside of enclosure 12. Controller 22 is responsive to both inside and ambient sensor units 18 and 20 to control the operation of conventional refrigerator unit 14 and auxiliary ambient air refrigerator unit 16. There may also be a humidifier 24 that may be controlled by controller 22 to keep the humidity within enclosure 12 within a desired range. Controller 22 responds to the sensor units and the indicated dew points of the enclosure and the ambient air and enables the auxiliary refrigerator unit to provide cool ambient air to the enclosure when the temperature inside the enclosure is above a first predetermined temperature, the ambient temperature is less than the temperature inside the enclosure by a predetermined differential temperature and the dew point of the ambient air is matched to the dew point range of the air in the enclosure. Controller 22 also responds to the sensor units 18 and 20 to enable the conventional refrigeration unit when the temperature is above a second predetermined temperature that is higher than the first predetermined temperature. The dew point range may include a minimum humidity dew point for the enclosure, in which case the auxiliary refrigeration unit will not be enabled if the dew point of the air inside the enclosure is below that minimum dew point and the dew point of the ambient air is not higher than the dew point of the air inside the enclosure. The dew point range may include a maximum humidity dew point and the auxiliary refrigeration unit in that case will not be enabled if the dew point of the air inside the enclosure is above that maximum dew point and the dew point of the ambient air is not lower than the dew point of the air inside the enclosure. Sensor units 18 and 20 may include a temperature sensor and a humidity sensor from which controller 22 calculates the dew point. Or the temperature humidity sensors 18 and 20 may actually include a dew point meter to directly provide the dew point to controller 22.

One source defines a dew point as the temperature to which a given parcel of humid air must be cooled at a constant barometric pressure for water vapor to condense into water. The dew point is actually a saturation temperature. Dew point is closely associated with relative humidity. A high relative humidity indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates that the dew point is equal to the current temperature and the air is maximally saturated with water. When the dew point remains constant and temperature increases relative humidity will decrease. Dew point meters are used to measure dew point over a wide range of temperatures. One version of such meters can consist of a polished metal mirror which is cooled as air is passed over it. The temperature is monitored and the temperature at which the dew forms is by definition the dew point. In fact, these devices are often used to calibrate other types of humidity sensors. If controller 22 receives a dew point reading directly from sensor units 18 and 22 it is unnecessary to calculate the dew point. But if controller 22 receives temperature and relative humidity it may calculate the dew point according to a well known approximation which calculates the dew point T_(d) given the relative humidity RH and the actual temperature T of the air. That approximation is as follows:

$T_{d} = \frac{b\; {\gamma \left( {T,{RH}} \right)}}{a - {\gamma \left( {T,{RH}} \right)}}$

where

${\gamma \left( {T,{R\; H}} \right)} = {\frac{a\; T}{b + T} + {\ln \left( {R\; {H/100}} \right)}}$

where the temperatures are in degrees Celsius and “In” refers to the natural logarithm. The constants are:

a=17.271

b=237.7° C.

There is also a very simple approximation that allows conversion between the dew point, the dry-bulb temperature and the relative humidity. This approach will be accurate to within about ±1° C. as long as the relative humidity is above 50%.

The equation is:

$T_{d} = {T - \frac{100 - {R\; H}}{5}}$

or

RH=100−5(T−T _(d)).

This can be expressed as a simple rule of thumb: For every 1° C. difference in the dew point and dry bulb temperatures, the relative humidity decreases by 5%, starting with RH=100% when the dew point equals the dry bulb temperature and where in this case RH is in percent, and T and T_(d) are in degrees Celsius.

Controller 22 may be a hard wired apparatus as shown in one specific embodiment in FIGS. 2 and 3 or it may be a properly configured microprocessor such as a Freeaire® Cooler Controller™ model 2100.

In one mode of operation there may be set a maximum allowable relative humidity within an enclosure 12 (MAX humidity) and a minimum allowable relative humidity (MIN humidity). Controller 22 monitors and compares the temperature and the relative humidity or dew point of both the enclosure (inside) and the ambient (outside) air at all times. The outside or ambient air system operates based on temperature until either the MAX or MIN humidity is reached. After that ambient air is only brought into the space if the relative humidity of the outside air is such that it would improve or match the relative humidity in the enclosure once it warms to the temperature inside the enclosure 12. Controller 22 thus either calculates the dew point or is delivered a sensed dew point. If the inside space is already too dry, the controller 22 would not bring in the ambient air if the ambient air dew point is lower that the enclosure air dew point. If the air inside enclosure 12 is already too humid, controller 22 would not bring in outside air if its dew point is higher than the dew point of the enclosure air. Generally, if there is a range of acceptable humidity with a minimum humidity for a given enclosure temperature and the enclosure air is already too dry then no ambient air with a dew point temperature lower than that of the enclosure air can be used even if it is at 100% relative humidity. Contrastingly, if there is a maximum acceptable humidity for a given enclosure temperature and the enclosure air is already too humid then all ambient air with a dew point temperature lower than the enclosure air can be used if it is cold enough and even if it is at 100% relative humidity. To protect the minimum humidity range when the ambient air dew point is lower than the minimum humidity, controller 22 may activate a humidifier 24 to add moisture to the space or the humidifier could be provided with its own controls so the two systems are completely separate. With the humidifier 24 the outside air could be used even if it contained low humidity.

Referring to FIG. 2, there is shown an insulated refrigerated enclosure 101 with an outside wall 102 which separates the enclosure 101 from the outside atmosphere, and an inside wall 103 that separates the enclosure 101 from a mechanical room 104. The present invention is not limited to the specific conditions herein described; there are many different situations in which the present invention would work well, including the case in which the enclosure is separated from the ambient or outside atmosphere by another room and the case in which the mechanical “room” is in the outside atmosphere. What is herein described is a typical situation in which a refrigerated enclosure such as a walk-in cooler or storage room is located in a building such as a grocery store or restaurant and is in a climate where the outside air temperature is cold enough to be used for refrigeration for a significant portion of the year.

In FIG. 2 there is also shown a conventional refrigeration system including an evaporator 105, with three identical evaporator fans 106 and evaporator coils (not shown), a refrigerant liquid line 108, a liquid line solenoid valve 109, an expansion valve 110, and a refrigerant suction line 111 inside the enclosure 101, and a compressor 112, a condenser 113, a condenser fan 114, and a low pressure control 115 inside the mechanical room 104. The conventional refrigeration system also includes the addition of a circulating fan 116 which is attached to the inside wall 103 by bracket 117.

The auxiliary outside or ambient air refrigeration system includes an intake damper housing 118 that has a pair of insulated dampers 120, a gasket 121, and a damper closure spring (not shown), mounted on the inside surface of the outside wall 102, in line with a first airflow passage 123 through the outside wall 102. On the outside surface of the outside wall 102, in line with the airflow passage 123, is mounted the outside air fan 124, which is contained in an outside air fan housing 125. The outside air fan housing 125 also houses a filter 126, which is removable by sliding the filter 126 along the filter track 127. Elsewhere on the outside surface of the outside wall 102, in line with a second airflow passage 130, is an enclosure air fan 128, that has a finger guard (not shown) mounted on its face. In line with the second airflow passage 130, on the outside surface of the outside wall 102 is an outside wallcap 131 that surrounds the enclosure fan 128, that is mounted to the end of an exhaust damper housing 132 extending through the wall 102 to its inside face to which it is mounted and which ends with a pair of insulated outward-opening dampers 133, a gasket 134, and a damper closure spring 135.

The controller 136 is mounted on the inside surface of the outside wall 102 and is connected to a source of power through four electrical conductors, 137, 138, 139, and 140. The controller 136 is also connected electrically to the outside air fan 124 by an electrical conductor 141, to the enclosure air fan 128 by the electrical conductor 142, to the liquid line solenoid valve 109 by the electrical conductor 143, to the evaporator fans 106 by the electrical conductor 144, and to the circulating fan 116 by electrical conductor 145. Also, the controller 136 is electronically connected to an inside temperature and dew point sensor unit 146 mounted on the inside surface of the wall 102 near the controller 136, by a low voltage conductor 147, and to an outside ambient temperature and dew point sensor unit 148, mounted on the outside surface of the outside wall 102, by a low voltage conductor 149 which passes through a hole 150 in the outside wall 102.

In FIG. 3, there is shown a schematic wiring diagram of the auxiliary ambient air refrigeration system in combination with the conventional refrigeration system. Components of the conventional refrigeration system include the compressor 112 and the condenser fan 114 both of which are in series with the low pressure control 115. The controller 136 is powered by electricity through electrical conductor 137 and is controlled by an on/off switch 151. A “power on” light 152 is in series with the switch 151. Also in series with the switch 151 is a circuit connecting a differential thermostat 153, an inside thermostat 154 for the ambient air refrigeration system, and the coil 157 of an ambient air refrigeration system relay 156. The circuit made by the electrical conductors 138 and 141 and the outside air fan 124 and the circuit made by the electrical conductors 138 and 142 and the enclosure air fan 128 are both controlled by the normally open contacts 158 of the relay 156. Another component in series with the switch 151, and in parallel to the outside air refrigeration system control circuit, is the inside thermostat 155 for the conventional refrigeration system. The inside temperature and dew point sensor unit 146 supplies the temperature information about the air temperature inside the enclosure to the inside thermostat 155 for the conventional refrigeration system as well as for the differential thermostat 153 and the inside thermostat 154 for the outside air refrigeration system as well as dew point information. The outside or ambient temperature and dew point sensor unit 148 supplies temperature information to the differential thermostat 153 as well as dew point information. The coil 160 of the conventional refrigeration system relay 159 and the coil 163 of the time-delay relay 162 are in series with the thermostat 155 and switch 151, but are in parallel with each other. The circuit made by electrical conductors 139 and 143 and the liquid line solenoid valve 109 is controlled by the normally open contacts 161 of the relay 159. The circuit made by electrical conductors 140 and 144 and the evaporator fans 106 is controlled by the normally open contacts 164 of the time-delay relay 162. The circuit made by the electrical conductors 140 and 145 and the circulating fan 116 is controlled by the normally closed contacts 165 of the time-delay relay 162.

The components of the conventional refrigeration system are arranged so as to extract heat from the enclosure 101 and transfer it to the mechanical room 104. The On/off switch 151 must be in the “on” (closed) position. The inside thermostat 155 in the controller 136 replaces the thermostat which would normally control the operation of the conventional refrigeration system. When the inside temperature and dew point sensor unit 146 senses that the temperature of the air is at or above the predetermined cut-in temperature setting for the conventional refrigeration system (typically 38 degrees F.), the inside thermostat 155 closes, energizing the coil 160 of the relay 159 which closes the normally open contacts 161 making an electrical circuit through the electrical conductor 139 and 143 which energizes the liquid line solenoid valve 109. This allows liquid refrigerant to move through the refrigerant liquid line 108 and the expansion valve 110 to enter the evaporator coils and evaporate. The evaporation of the refrigerant inside the evaporator coils extracts heat from the enclosure air flowing past the evaporator coils as a result of the operation of the evaporator fans 106.

The process continues until the enclosure 101 is sufficiently cooled that the inside temperature and dew point sensor unit 146 senses that the air temperature has dropped to the predetermined temperature representing the cut-out temperature setting for the conventional refrigeration system (typically 36 degrees F.) This, in turn, causes the inside thermostat 155 to open, which de-energizes the coil 160 of the conventional refrigeration system relay 159, which causes the normally open contacts 161 to open, which de-energizes the liquid line solenoid valve 109, causing it to close. As the compressor 112 continues to operate the evaporated refrigerant is pumped out of the refrigerant suction line 111, which causes the pressure in it to drop until it reaches a predetermined pressure representing the cutout pressure setting for the compressor. This causes the low-pressure control 115 to de-energize the compressor 112 and condenser fan 114.

When the inside sensor 46 senses the temperature inside the enclosure 101 has risen to the predetermined cut-in temperature setting for the conventional refrigeration system (typically 38 degrees F.), causing the inside thermostat 155 to close, the coil 163 of the time-delay relay 162 is energized. This causes the normally open contacts 164 to close, thereby energizing the evaporator fans 106, and the normally closed contacts 165 to open, thereby de-energizing the circulating fan 116. When the enclosure temperature drops to the predetermined cut-out temperature setting of the conventional refrigeration system (typically 36 degrees F.), the inside thermostat 155 opens, the coil 163 of the time-delay relay 162 is de-energized. After a predetermined delay, the normally open contacts 164 open, de-energizing the evaporator fans 106, and the normally closed contacts 165 close, energizing the circulating fan 116. The predetermined delay in the operation of the contacts 164 and 165 of the time-delay relay 162 is user-adjustable to allow for shortening the period of time the evaporator fans 106 operate and extending the period of time the circulating fans 116 operate in order to reduce energy use, and for extending the period of time the evaporator fans 106 operate in order to allow more heat transfer to the evaporator coils.

The ambient air refrigeration cycle begins, FIGS. 2 and 3, when the outside sensor unit 48 senses that the temperature of the outside atmospheric air is cooler than a pre-selected number of degrees cooler than the temperature of the air inside the enclosure 101, sensed by the inside temperature and dew point sensor unit 146, which represents the cut-in temperature differential for the outside air refrigeration system (typically 6 degrees F.). This causes the differential thermostat 153 to close. When the inside temperature and dew point sensor unit 146 also senses that the temperature inside the enclosure 101 is at or above the cut-in temperature setting for the outside air refrigeration system (typically 36 degrees F.), this causes the inside thermostat 154 for the outside air refrigeration system to also close. Since both the thermostats 153 and 154 and the switch 151 are in series, when they are all in a closed position they cause the coil 157 of the outside refrigeration system relay 156 to be energized. This, in turn, causes the normally open contacts 158 to close, which energizes the outside air fan 124 (through electrical conductors 138 and 141) and the enclosure air fan 128 (through electrical conductors 138 and 142).

When the outside air fan 124 is energized it draws outside atmospheric air through the filter 126 into the outside air fan housing 125. The air is then forced through the first airflow passage 123 and the inside wall-cap base 119 where the force exerted by the incoming air overcomes the force exerted by the damper closure spring 122 and opens the damper 120 allowing the outside air to pass through the intake damper housing 118 and enter the enclosure 101. When the enclosure air fan 128 is energized, it draws air from the enclosure 101, through the finger guard 129 and forces the air into the second airflow passage 130 and through the exhaust damper housing 132 where the force exerted by the air overcomes the force exerted by the damper closure spring 135 and opens the damper 133 allowing the enclosure air to flow through the outside wallcap 131 into the outside atmosphere.

The simultaneous operation of the two fans 124 and 125 results in a gradual lowering of the air temperature within the enclosure. When the inside temperature and dew point sensor unit 146 senses that the air temperature within the enclosure has reached the predetermined cut-out temperature setting for the outside air refrigeration system (typically 34 degrees F.), the inside thermostat 154 opens, which de-energizes the coil 157 of the relay 156, which opens the normally open contacts 158, which, in turn, de-energizes the fans 124 and 128, stopping the flow of outside air into and out of the enclosure 101. The operation of the two fans 124 and 128 is also stopped when the outside temperature and dew point sensor unit 148 senses that the outside temperature has risen (or the inside temperature has dropped) so as to make the outside temperature warmer than a predetermined number of degrees cooler than the inside temperature, as sensed by the inside temperature and dew point sensor unit 146, which represents the cut-out temperature differential setting for the outside air refrigeration system (typically 4 degrees F.), which causes the differential thermostat 153 to open, de-energizing the coil 157 of the relay 156, causing the contacts 158 to open and thereby de-energizing the fans 124 and 128.

The cut-out temperature differential setting for the outside air refrigeration system is selected so as to cause the operation of the fans 124 and 128 when the amount of cooling provided by those fans is greater than the amount of cooling provided by the conventional refrigeration system while consuming an equal amount of electrical energy. The “breakeven point” at which the outside air refrigeration system is equally as energy efficient as the conventional refrigeration system is typically reached when the outside air temperature is about 4 degrees F. cooler than the temperature inside the enclosure. Therefore, a differential of about 4 degrees is the smallest differential that should be used in order to minimize the use of energy.

The cut-in temperature differential is selected so as to maximize the operation of the outside air refrigeration system without causing unacceptable short-cycling of the fans 124 and 128. A relatively small hysteresis, or difference between the cut-in and cut-out temperature differential settings, typically about 2 degrees F., is all that is needed. A larger hysteresis leads to unnecessary loss of operation of the outside air system and a smaller hysteresis can result in the fans 124 and 128 cycling on and off too frequently.

Because when the outside air refrigeration system operates it is more efficient than the conventional refrigeration system, to minimize energy use it is necessary to operate the conventional system only when the outside air system cannot maintain a cool enough temperature inside the enclosure. This is accomplished by having the inside thermostat 155 for the conventional refrigeration system have a higher operating temperature range than the inside thermostat 154 for the outside air refrigeration system. Typically, for inside thermostat 155 for the conventional system, the cut-in temperature setting is 38 degrees F. and the cut-out setting is 36 degrees F., and for the inside thermostat 154 for the outside air system, the cut-in temperature setting is 36 degrees F. and the cut-out setting is 34 degrees F. As long as the outside air system can keep the temperature inside the enclosure from rising to 38 degrees F. the conventional system will not operate.

In FIG. 2 and temperature and dew point sensor units 146 and 148 provide inputs to the controller 136 to see that the auxiliary ambient air refrigeration unit operates only when the temperature inside the enclosure is above a first predetermined temperature, the ambient temperature is less than the enclosure temperature by a predetermined differential temperature and the dew point of the ambient air is matched to the dew point range of the air in the enclosure. For more details see U.S. Pat. No. 5,239,834 incorporated herein in its entirety by this reference.

Controller 136 operates to control humidity in the enclosure when supplying ambient (outside) air as shown in FIGS. 4 and 5. This humidity control is in addition to and simultaneous with the temperature control just described. The ambient air fans will operate only when both the humidity control and the temperature control allow it. FIG. 4 is the logic diagram for providing ambient air whose humidity is matched to that of the range of the humidity in the enclosure when there is a minimum humidity control. FIG. 5 does the same when there is a maximum humidity control. In FIGS. 4 and 5 the following acronyms are used: RH=Relative Humidity, IH−Inside (relative) Humidity, IHMIN=Inside Humidity Minimum setting (default: 0%), IHMAX=Inside Humidity Maximum setting (default: 100%), IDP=Inside Dew Point temperature, and ODP=Outside Dew Point temperature. In FIG. 4 the cycle begins with the outside air fans off, 200. The inside humidity or dew point is read, 202, and a determination is made as to whether it is moist enough inside (IH>IHMIN+1% RH), 204. If it is, the outside fans are allowed to turn on, 206; if it is not the inside and outside humidity or dew points are read and the IDP and ODP are calculated, 208. Then it is determined whether it is moist enough outside (ODP>IDP+1° F.), 210. If it is not, then the outside fans are left off, 212, and the cycle returns to read the inside humidity or dew point at 202; if it is moist enough outside, in condition 210, then the outside air fans are allowed to turn on, 214. With the fans on the inside humidity or dew point is determined, 216; if it is moist enough inside (IH>IHMIN), 218, the outside fans are left on, 220. If it is not moist enough inside the IDP and ODP are calculated, 222, and then inquiry is made again as to whether is it moist enough outside (ODP>IDP), 224. If it is not, the outside air fans are turned off, 226; if it is, the outside fans are left on, 228.

The maximum humidity control with outside air cycle begins in FIG. 5 with the outside air fans off, 240. The inside humidity or dew point sensor is read, 242; if it is dry enough inside (IH<IHMAX−1% RH), 244, the outside air fans are allowed to turn on, 246. If it is not, the inside and outside humidity or dew points are read and the IDP and ODP are calculated, 248. If it is dry enough outside (ODP<IDP−1° F.), 250, the outside air fans are allowed to turn on, 252; if it is not, the outside air fans are left off, 254. When the outside air fans are on the inside humidity or dew point is read, 256; if it is dry enough inside (IH<IHMAX), 258, the outside air fans are left on, 260. If it is not, the IDP and ODP are calculated again, 262, then the inquiry is made again, if is it dry enough outside (ODP<IDP), 264. If it is not, the outside air fans are turned off, 266; if it is dry enough outside the outside air fans are left on, 268.

An alternative approach for humidity control combining both maximum and minimum humidity logic is shown in FIG. 6. Initially the dry-bulb temperature logic calls for outside air, 300. Inquiry is then made as to whether the outside air fans are on, 302. If the response is yes the next decision point is: is inside humidity<minimum humidity set point, 304. If the response is yes, inquiry is made as to whether the outside dew point is <inside dew point, 306. If the response here is no or the response in step 304 is no then inquiry is made as to whether the inside humidity is >maximum humidity set point, 308. If the response is yes, inquiry is made as to whether the outside dew point>the inside dew point, 310. If the response is no or if the response was no to step 308 the outside fans are turned on 312. If in step 302 it is noted that the outside fans are not on, then inquiry is made as to whether the inside humidity is <(minimum humidity set point+ΔH), where ΔH is the hysteresis effect step 314. If the response is yes, inquiry is made as to whether the outside dew point is <the inside dew point+ΔDP where ΔDP is again a factor of hysteresis, 316. If the response here is no, or the response to step 314 was no inquiry is made as to whether the inside humidity is >(maximum humidity set point−ΔH), 318. If the answer is yes, inquiry is made as to whether the outside dew point>(inside dew point−ΔDP), 320. If the response is no, or the response to step 318 was no, the outside air fans are turned on, 322. If the response in either step 306 or 316 is yes or the response step 310 or 320 is yes, the outside air fans are turned off, 324.

Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments.

In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.

Other embodiments will occur to those skilled in the art and are within the following claims.

What is claimed is: 

1. An auxiliary ambient air refrigeration system for cooling and controlling humidity in an enclosure comprising: a conventional refrigeration unit for providing cool refrigerated air to the enclosure; an auxiliary refrigeration unit for providing cool ambient air to the enclosure; a first sensor unit for sensing air temperature and humidity inside the enclosure; a second sensor unit for sensing ambient air temperature and humidity; and a controller responsive to said sensor units and their indicated dew points of the enclosure air and the ambient air for enabling said auxiliary refrigeration unit to provide cool ambient air to the enclosure when temperature inside the enclosure is above a first predetermined temperature, the ambient temperature is less than the enclosure temperature by a predetermined differential temperature and the dew point of the ambient air is matched to the dew point range of the air in the enclosure.
 2. The auxiliary ambient air refrigeration system of claim 1 in which said controller is responsive to said sensor units for enabling said conventional refrigeration unit when the enclosure temperature is at a second predetermined temperature higher than said first predetermined temperature.
 3. The auxiliary ambient air refrigeration system of claim 1 in which said dew point range includes a minimum humidity dew point and the auxiliary refrigeration unit is not enabled if the dew point of the enclosure air is at or below that minimum dew point and if the dew point of the ambient air is below the dew point of the enclosure air.
 4. The auxiliary ambient air refrigeration system of claim 1 in which said dew point range includes a maximum humidity dew point and the auxiliary refrigeration unit is not enabled if the dew point of the enclosure air is at or above that maximum dew point and if the dew point of the ambient air is above the dew point of the enclosure air.
 5. The auxiliary ambient air refrigeration system of claim 3 further including a humidifier and said controller is responsive to a humidity below said minimum humidity dew point to enable said humidifier.
 6. The auxiliary ambient air refrigeration system of claim 1 in which each said sensor unit includes a temperature sensor and a dew point sensor.
 7. The auxiliary ambient air refrigeration system of claim 1 in which said dew point range includes a minimum humidity dew point and the auxiliary refrigeration unit is not enabled if the dew point of the ambient air is below that minimum dew point.
 8. The auxiliary ambient air refrigeration system of claim 1 in which said dew point range includes a maximum humidity dew point and the auxiliary refrigeration unit is not enabled if the dew point of the ambient air is above that maximum dew point. 